Crude oils predominantly contain hydrocarbons, with sulfur, nitrogen, oxygen, and metals being minor constituents. While it is desirable to recover the hydrocarbon constituents in their pure form, it is difficult to isolate pure products because most of the minor constituents occur in combination with carbon and hydrogen. Separation of impurities such as those listed above generally requires expenditures of valuable resources such as time, chemicals, energy, and money. Therefore, one goal of the petroleum processing industry is to optimize impurity-removal procedures, equipment, and resources in order to eliminate those impurities that have the most degrading effect on the end products.
A common impurity encountered in hydrocarbon processing is sulfur. The presence of sulfur in hydrocarbon products generally increases the corrosive characteristics thereof, and sulfur forms harmful and noxious reaction products upon combustion. Consequently, measures are taken to either reduce the amount of sulfur or to render the sulfur-containing compounds inoffensive. A common method for treating petroleum to reduce the degrading effects of sulfur is chemical processing to “sweeten” sulfur compounds contained in the particular fractions, e.g., mercaptans that are designated by the formula R—SH. “Sweetening” denotes that mercaptan sulfur compounds are converted to less objectionable disulfide compounds, e.g., R—S—S—R, R—S—S—R′, etc. One particular process known in the art is the sweetening of petroleum products such as kerosene by the MEROX® process, which is available from UOP LLC of Des Plaines, Ill., USA. MEROX is a proprietary process for the removal of mercaptans from a hydrocarbon stream.
In order to sweeten a petroleum product, a caustic solution, such as sodium hydroxide or potassium hydroxide, is generally first used to convert the mercaptan compounds to the ionic state, RS−. The caustic solution is also helpful in that it removes naphthenic acids and other organic acids in general such as phenolic acids, and other sulfur compounds from refined petroleum products and petroleum distillate. Unfortunately, since caustic solutions are quite harmful to organic tissue, extreme care must be taken in the use and disposal of caustic solutions in order to protect the waterways, rivers, subterranean water formations, and, in many places, the oceans and surrounding seas of industrial refining areas from caustic pollution. This presents a significant problem to the refining industry because of the great volume of caustic solutions used in petroleum processing and because all of the solutions used must eventually be discarded as a non-regenerative caustic solution or as the spent liquor resulting from a regenerative process.
To date, the industry generally uses two methods to dispose of spent caustic materials—neutralization and incineration, with incineration being a relatively new trend in waste caustic liquor disposal. Incineration disposal presents certain disadvantages, however. For example, the cost of operation of the incinerator units is high because of the energy required to maintain the elevated temperatures necessary to maintain combustion of the predominantly aqueous solution of alkaline waste. Commercial units presently in operation make use of the combustion of fuel oil and natural gas to sustain the evaporation of the aqueous parts of the waste liquor and then furnish mostly carbon dioxide, CO2, to form the innocuous carbonates of sodium or other alkali metals for disposal. Refined fuel oil and natural gas are very expensive for use in disposing of the volumes of caustics discarded as a result of petroleum processing and they are both very valuable commodities in terms of consumer-useable energy sources. As such, neutralization remains a desirable alternative to incineration.
Accordingly, it is desirable to provide systems and methods for treating caustic materials that do not primarily rely on the combustion of fuel oil or natural gas. It is further desirable to provide such systems and methods that neutralize the caustic materials to an acceptable level for disposal. Furthermore, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.